The present invention relates to a device for cooling semiconductors such as multi-chip modules mounting chips that generate large amounts of heat used for a large computer, and to a method of fabricating the same.
Various means have heretofore been studied for removing large amounts of heat generated from the circuits accompanying the development in the technology for highly densely packaging the integrated circuits on a substrate. In recent years, in particular, studies have been conducted concerning a thermal conduction liquid cooling which couples the heat generating portion to the cooling liquid through a thermal conduction path using a thermal conduction device in place of the conventional forced air cooling, and concerning a direct cooling by which the whole circuit is immersed in the coolant, in order to cool the integrated circuits that consume large amounts of electric power. The former system has been disclosed in, for example, Japanese Patent Laid-Open No. 53547/1977. According to this cooling device,, however, a large heat resistance develops between a chip and a piston, and between the piston and a housing.
According to U.S. Pat. No. 3,649,738 or Japanese Patent Laid-Open No. 44479/1979 furthermore, a system is disclosed in which a path through which a cooling fluid flows is provided in a cold plate that has a flexible surface such as bellows, and the cold plate that is cooled is brought into direct contact with the chip. Even according to this system, a large heat resistance develops on the contact surface between the chip and the cold plate imposing limitation on the ability for removing the heat generated by the chip, and making it difficult to adjust the cooling performance depending upon the amounts of heat generated by the individual chips.
In contrast with the above conduction cooling, a direct immersion cooling is disclosed in Japanese Patent Laid-Open No. 134451/1985, wherein finned chips mounted on a substrate are cooled by the forced convection of liquid that flows through the module. According to this system, the cooling can be affected efficiently owing to the forced convection. When the chips are arranged in line in a direction in which the cooling liquid flows, however, the temperature of the cooling liquid rises as it flows making it difficult to maintain the chips at a uniform temperature. When the chips are arrayed in a staggered manner, the packaging density decreases, the wiring length increases in the substrate for connecting the chips, and the signal processing speed becomes slow.
According to this cooling system in which the whole module is cooled, furthermore, no provision is made for allowing a change in the flow for each of the chips to change the cooling characteristics.
The above-mentioned U.S. Pat. No. 3,649,738 or U.S. Pat. No. 4,277,816 discloses a cooling method using an impinging jet. In the impinging jet, the heat transfer coefficient is the highest at the central position of impinging of jet and decreases rapidly toward the radial direction thereof as has been disclosed in, for example, Japan Society of Mechanical Engineers "JSME Data Book : Heat Transfer", 3rd Edition, February, 1975, p. 110. This means that when the chip is to be cooled using the impinging jet, the temperature becomes lower at the center of the chip than at the periphery, and noise generates due to a temperature difference in the chip.
A system for individually cooling the chips by the forced convection boiling using a liquid jet has been shown in FIG. 5 of Computers in Mechanical Engineering, Springer-Verlag, Vol. 6, No. 6, P. 18, 1988. This system is capable of removing a high heat flux. However, when the chips generate the heat in different amounts and when the heat must be removed in different amounts for each of the chips, it becomes necessary to change the flow rate, flow velocity and temperature of jet for each of the chips to uniformalize the temperature. Therefore, the same problems remain as those mentioned with reference to the above U.S. Pat. No. 3,649,738 or Japanese Patent Laid-Open No. 44479/1979.